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|Planoglobanomalina pseudoalgeriana Olsson & Hemleben 2006|
= Planoglobanomalina pseudoalgeriana
Current identification/main database link: Planoglobanomalina Olsson and Hemleben, 2006
Type of wall: Smooth, normal perforate.
Test morphology: Test asymmetrical to fully planispiral, compressed, loosely coiled, evolute to partially involute, oval in outline, chambers compressed, elongate, numerous chambers in ultimate whorl, last one to three chambers in ultimate whorl arranged in an uncoiling trend, apertural lips of chambers in the ultimate whorl fuse to form a somewhat broad shelf that extends around the umbilicus, relict apertures present where apertural lips are not completely fused; primary aperture equatorial, asymmetric to symmetric, an oval shaped opening bordered by a broad lip, test much compressed with a pinched periphery which gives the chambers an ogyval shape.
Size: Maximum diameter of type species 0.39 mm, thickness 0.12 mm.
Etymology: Named after Globanomalina, the ancestor of this genus and in recognition of its planispiral coiling.
Extra details from original publication
DISTINGUISHING FEATURES.—Planoglobanomalina n. gen. is distinguished from the homeomorphic genus Pseudohastigerina by its more compressed test, pinched periphery and ogyval-shaped chambers in edge view. Planoglobanomalina is more loosely coiled, more evolute, and the last few chambers show a tendency towards uncoiling. Pseudohastigerina is more tightly coiled, more involute, and develops bipartite, biumbilicate apertures in some specimens, in contrast to Planoglobanomalina, which has a single primary aperture and in some specimens relict apertures between fused apertural lips.
DISCUSSION.— Based on his study of the early Eocene KANE 9 core in the eastern equatorial Atlantic Ocean, Blow (1979) proposed that Pseudohastigerina danvillensis (Howe and Wallace) had an independent line of descent from other members of the genus, which he proposed was from Globorotalia (Turborotalia) planoconica Subbotina (= Globanomalina planoconica in this work), in contradiction to the views of Cordey and others (1969) who had considered P. danvillensis as a junior synonym of P. micra. He concurred with their view that P. micra had evolved from Pseudohastigerina wilcoxensis (Cushman) and that P. wilcoxensis, in turn, had evolved from Globanomalina at the base of Zone P6. Specialists have ignored Blow’s suggestion that there were two independent origins for the genus Pseudohastigerina. However, our examination of assemblages from ODP Hole 865B from the equatorial Pacific and recent drill-cores from Tanzania (Pearson and others, 2004) confirm Blow’s earlier observations of a separate origin for a planispiral morphotype in the early Eocene that is morphological similar to Pseudohastigerina. This necessitates the naming of a new genus, because unlike Blow (1979) we do not permit polyphyletic form-genera in our classification.
Blow derived Pseudohastigerina danvillensis from Globorotalia (Turborotalia) planoconica (=Globanomalina planoconica) and illustrated specimens of G. planoconica from Zone E8 (see discussion below on the taxonomy of planoconica) that showed apertures that extended slightly onto the spiral side as well as specimens of P. danvillensis showing equatorial apertures. His observations do indeed illustrate a linkage between these Eocene morphotypes of G. planoconica and the derivation of a planispiral morphology. He was, however, incorrect in his identification of Pseudohastigerina danvillensis, which is a junior synonym of Pseudohastigerina micra (see discussion below). We have also observed a similar transitional morphology in ODP Hole 865B and Tanzania Drilling Project Site 2, but starting in Zone E6. The planispiral morphotype is more openly coiled and planispirally evolute with a tendency towards uncoiling of the last few chambers in the ultimate whorl (Plate 14.2, Figs. 5, 8-10). The test is much compressed and the chambers in axial view have a pinched periphery and show an ogyval shape that Blow emphasized as a distinguishing characteristic in separating his P. danvillensis (=P. micra) from P. micra. Morphotypes with 9 to 10 elongated chambers in the ultimate whorl are closely homeomorphic with the Aptian planispiral species Globigerinelloides algerianus (Plate 14.2, Fig. 5). These morphotypes do not appear to range above Zone E8. Other characteristics of all these morphotypes include recurved sutures and somewhat broad apertural lips that fuse with previous lips to form an apertural rim around the umbilicus. In some specimens, as was noted by Blow, relict apertures open where the lips are not completely fused. The planispiral to almost planispiral morphotypes derived from Globanomalina planoconica are herein placed in the new genus Planoglobanomalina and the type species for the new genus is the new species Planoglobanomalina pseudoalgeriana.
PHYLOGENETIC RELATIONSHIPS.— Planoglobanomalina n. gen. evolved from Globanomalina planoconica and left no descendants.
STRATIGRAPHIC RANGE.— Zone E6 to Zone E8.
GEOGRAPHIC DISTRIBUTION.— Global in low and mid latitudes
STABLE ISOTOPE PALEOBIOLOGY.— no data available.
Blow, W. H. (1979). The Cainozoic Globigerinida: A study of the morphology, taxonomy, evolutionary relationships and stratigraphical distribution of some Globigerinida (mainly Globigerinacea). E. J. Brill, Leiden. 2: 1-1413. gs Olsson, R. K. & Hemleben, C. (2006). Taxonomy, biostratigraphy, and phylogeny of Eocene Globanomalina, Planoglobanomalina n. gen and Pseudohastigerina. In, Pearson, P. N., Olsson, R. K., Hemleben, C., Huber, B. T. & Berggren, W. A. (eds) Atlas of Eocene Planktonic Foraminifera. Cushman Foundation for Foraminiferal Research, Special Publication. 41(Chap 14): 413-432. gs V O
Blow, W. H. (1979). The Cainozoic Globigerinida: A study of the morphology, taxonomy, evolutionary relationships and stratigraphical distribution of some Globigerinida (mainly Globigerinacea). E. J. Brill, Leiden. 2: 1-1413. gs
Olsson, R. K. & Hemleben, C. (2006). Taxonomy, biostratigraphy, and phylogeny of Eocene Globanomalina, Planoglobanomalina n. gen and Pseudohastigerina. In, Pearson, P. N., Olsson, R. K., Hemleben, C., Huber, B. T. & Berggren, W. A. (eds) Atlas of Eocene Planktonic Foraminifera. Cushman Foundation for Foraminiferal Research, Special Publication. 41(Chap 14): 413-432. gs V O
Planoglobanomalina compiled by the pforams@mikrotax project team viewed: 17-9-2021
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